1. Field of the invention
The invention relates to a powder supply device for use in the formation of coatings by laser beam treatment.
2. Summary of the Prior Art
Methods for forming coatings by supplying powder and causing it to melt using an energy beam, particularly a laser beam, have been widely developed. Examples of such methods are disclosed in FR-A-2 605 310; EP-A-0 212 938; EP-A-0 213 498 and GB-A-2 184 380.
The equipment used generally comprises a powder supply device which is similar in principle to the powder dispensers previously known and used in the formation of plasma flame spray coatings and operating using a carrier gas, generally a neutral gas such as argon, at a specific pressure and rate of flow as a vehicle for the powder. However, such methods have given rise to problems when applied to the formation of coatings using laser beams. In particular, the high speed of the powder particles entrained by the carrier gas gives rise to losses and wastage of powder, and the intersections of the laser beam and the material are disturbed by blowing problems.
Attempts to improve these earlier devices have been proposed. Thus, U.S. Pat. No. 4 270 675 describes a powder dispenser in which the evenness of flow is ensured by a rod connected to a vibrator. FR-A-2 452 528 provides a control device regulating the admission of the powder particles into a tube through which the carrier gas flows. U.S. Pat. No. 4 730 093 and U.S. Pat. No. 4 743 733 describe a device comprising a volumetric wheel associated with the reservoir and a powder supply pipe fitted with an air vibrator. EP-A-0 173 654 provides for a control of the powder supply parameters.
However, none of these known solutions is fully satisfactory, and in some particular applications the problems mentioned above are not properly solved by the use of the proposed equipment. Accordingly, it is an object of the invention to provide a device which makes it possible to deliver the powder to a chosen point in relation to the laser energy beam in localized manner and at a low particle speed, thus avoiding the drawbacks referred to above, especially inadequate yield due to powder losses and the risk of blowing disturbances which would be detrimental to the quality of the results.